Michihiro Yamagata

Efficiency Simulation for Diamond-Turned Diffractive Lenses

Diffraction efficiencies of hybrid diffractive-refractive lenses fabricated by the diamond turning process are discussed. Since the tip of a diamond tool has a certain nose radius, the relief profiles are rounded by the diamond turning process. Consequently, fabricated lenses have different diffraction efficiencies from their design. A computer simulation software based on the scalar diffraction theory was developed to calculate the diffraction efficiency of diamond-turned hybrid lenses. Hybrid achromatic lenses for optical pickups are simulated and measured. For a 10 µm nose radius, simulation results showed a diffraction efficiency of 82%. The difference in diffraction efficiency between simulation results and measurement results was less than 2%. Dual focus object lenses for compact disk (CD) and digital versatile disk (DVD) compatible pickups were also simulated. The difference in diffraction efficiency for our developed relief profile was small enough even with a 50 µm process.

Lens Design for Optical Head Compatible with Compact Disk and Digital Versatile Disk

This paper describes three approaches to lens design for reading different thickness disks with one optical system. In the case of an optical head using two different objectives with one actuator, the skew adjustments for both lenses are difficult. First we design objective lenses that are coma free against skew adjustment. The method that uses one objective lens with a liquid crystal shutter still results in a spherical aberration of 50 mλ for a 1.2 mm disk. Second, we design the inner area of the lens for a disk thickness of 0.9 mm, and then the spherical aberration becomes half. The third order spherical aberration of the entire aperture is made to be zero. Grating is integrated onto the surface of a dual focus lens, it causes stray light. We propose a grating profile that reduces stray light to one-fifth.

Proposal of Micro-Trichroic Structures for High-Sensitivity Color Image Sensors

We propose a micro-trichroic structure based on multiplexed Bragg reflectors. Employing such a structure on each image sensor (IS) cell can enhance the ability of color ISs. Numerical calculations confirm the feasibility of the proposed structure. We also emulated a structure with several layers, and reduced the number of layers substantially by decreasing the diffraction angles.

Inner Area Aberration Compensating Lens for Compact Disc (Compact Disc-Recordable)-Digital Versatile Disc Compatible Head

We have developed a dual-wavelength digital versatile disc(DVD)/compact disc(CD)-compatible inner area aberration compensating lens capable of reading compact disc-recordable (CD-R) disks. In order to be able to read CD and CD-R disks with an infrared laser, it is essential to increase the numerical aperture (NA) of the inner area, but the resulting deterioration of the read signal has been a problem. Performance levels that enable DVD disks to be read have been achieved by reducing the fifth-order spherical aberration (SA5) by means of a phase step.